| A | B |
|---|
| volcano | a weak spot in the Earth's crust where magma has comes to the surface and flows |
| magma | the molten mixure of rock-forming substances, gases, and water that make up part of the Earth's mantle |
| lava | liquid magma that reaches the surface |
| Ring of Fire | a major belt of volcanoes that sits around the rim of the Pacific Ocean |
| hot spot | an area where magma from deep within the mantle melts through the crust above it like a blow torch |
| island arc | a string of islands formed by the volcanoes occurring along a deep ocean trench |
| igneous rock | rock formed by molten magma or lava that has cooled |
| divergent plate boundary | a tectonic plate boundary where two plates move away from each other |
| convergent plate boundary | a tectonic plate bounadary where two plates move towards each other |
| pipe | a long tube through which magma moves fromthe magma chamber to the Earth's surface |
| magma chamber | the pocket beneath a volcano where magma collects |
| lava flow | the area covered by lava as it pours out of a volcano's vent |
| crater | a bowl-shaped area that forms around a volcano's central opening or vent |
| vent | the opening at the top of a volcano through which molten rock and gas leave |
| side vent | a vent that opens on the side of a volcano |
| silica | a material made of the elements silicon and oxygen that is found in magma |
| quiet eruption | occurs when thin, runny lava flows quickly and quietly from a vent |
| pahoehoe flow | a hot, fast-moving type of lava that cools and hardens to form wrinkles and rope-like coils |
| aa flow | a cooler, slow moving flow that hardens to form rough chunks |
| pyroclastic flow | the eruption of ash, cinders, bombs, and gases during an explosive volcanic eruption |
| active volcano | a volcano that is erupting or shows signs of erupting in the near future |
| dormant volcano | a volcano that does not show signs of erupting in the near future, but that still could erupt at some point |
| extinct volcano | a volcano that is unlikely to ever erupt again |
| hot springs | a pool formed by groundwater that is heated by a nearby mass of magma, and then rises to Earth's surface |
| geyser | a type of hot spring that builds up pressure underground and then erupts at regular intervals |
| geothermal energy | heat energy from inside the Earth that has been heated by magma |
| shield volcano | a wide, gently sloping mountain formed by quiet eruptions |
| cinder cone volcano | a steep-cone shaped hill made of volcanic ash, cinders, and bombs piled around the opening |
| composite volcano | a tall, cone-shaped mountain made of layers of lava and layers of ash and other volcanic materials |
| lava plateau | a high, flat area formed by lava flows from several long cracks in an area |
| caldera | a large hole at the top of a volcano formed when the roof of a volcano's magma chamber collapses |
| ash | small sand-sized pieces of volcanic rock |
| cinders (lapilli) | pebble-sized pieces of rock ejected from a volcano |
| bombs | chunks of ejected lava |
| volcanic neck | a deposit of hardened, cooled magma that gets stuck in a volcano's pipe |
| dike | a slab of volcanic rock formed when magma crosses rock layers |
| sill | a slab of volcanic rock formed when magma squeezes horizontally between layers of rock |
| batholiths | a mass of rock formed when magma cools inside the crust |
| dome mountains | when magma that is rising under the Earth is blocked by overlying rock, the pressure causes the layers of rock to bend upward, forming an arch or dome |
| explosive eruption | caused by thick, sticky magma that slowly builds up in the volcano's pipe until the pressure causes a very forceful explosion |
